References
The following references are cited as pertinent to the background of the invention, or as providing guidance in practicing the invention.                Ballica, R., et al., J Bone Miner Res, 1999, 14(7):1067.        Bird, C E, et al., J Clin Endocrinol Metab, 1978, 47(4):818.        Born, A K, Horm Metab Res, 1999, 31(8):472.        Boulanger, Y., et al., Int J Pept Protein Res, 1996, 47(6):477.        Buckley L M, et al. J Rheumatol, 1997, 24: 1489-94.        Cardona, J M, et al/, Osteoporos Int, 1997, 7(3):165.        Cerovsky, V. et al., Eur J. Biochem, 1997, 247(1):231.        Cornish, J., et al., Biochem Biophys Res Commun, 1995, 207(1):133.        Cornish, J., et al., Am J. Physiol, 1998, 275(4Pt1):E694.        Downs R W et al. J Bone Mineral Res, 1999; suppl 1, p S401 (abstract).        Epand, R M, et al., Int J Pept Protein Res, 1986, 27(5):501.        Hakala, J M, et al., Protein Eng, 1996, 9(2):143.        Heinz, D., et al., Steroids Lip Res, 1974, 5(4):216.        Jablonski, G., et al., Calcif Tissue Int, 1995, 57(5):385.        Kanis, J A, et al. J Bone Miner Res, 1994; 9: 1137-1141.        Katahira, R., et al., Int J Pept Protein Res, 1995, 45(5):305.        Laan, R F, et al., Ann Intern Med, 1993, 119(10):963.        Labrie, F. Mol Cell Endocrinol 1991, 78:C113-C118.        Labrie, F, et al. Ann N Y Acad Sci, 1995, 774:16-28.        Labrie, F, et al., J Clin Endocrinol Metab, 1997, 82(8):2403.        Looker A C, et al., J Bone Miner Res, 1995, 10(5):796-802.        Morfin, R., et al., J Steroid Biochem Mol Biol, 1994, 50(1-2):91.        NIH Press Release, Feb. 11, 1998.        Pozvek, G., et al., Mol Pharmacol, 1997, 51(4):658.        Romero, D F, et al., Calcif Tissue Int, 1995, 56(1):54.        Rosen, C J et al., J Bone Mineral Res, 1999;14 supp 1, pS400 (abstract).        Stroop, S D, et al., Endocrinology, 1996, 137(11):4752.        Suva, L J, et al., J Pharmacol Exp Ther, 1997, 283(2):876.        Uda, K., et al., Biol Phar Bull, 1999, 22(3):244.        Van Staa, T P, et al, Bone, 1998; 23 (5) supplement, S202 (abstract).        Vignery, A., et al., Bone, 1996, 18(4):331.        WHO Technical Report Series 843: Assessment of fracture risk and its application to screening for postmenopausal osteoporosis. Geneva, World Health Organization, 1994.        Wimalawansa, S J, et al., Crit Rev Neurobiol, 1997 11(2-3):167.        Young J, et al., J Clin Endocrinol Metab, 1997, 82:2578-2585, 1997.        
Osteoporosis is a “systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase of bone fragility and susceptibility to fracture.” It is the consequence of imbalance between bone formation (anabolic) and resorption of bone, with the latter predominating.
Following the first trimester of fetal development, bone growth is rapid. Multiple factors may regulate in utero transplacental calcium transport and in utero bone formation, including but not limited to vitamin D, calcitonin, parathyroid hormone, and miscellaneous growth factors. In humans, bone mass peaks at approximately the end of the second decade of life and declines thereafter. The cause of the shift from predominantly bone formation in early life to bone resorption in later life is unknown.
The NIH has stated that “osteoporosis is an important and potentially growing public health problem in which weakened bones are easily fractured. More than 1.3 million hip, spine and wrist fractures each year are attributable to osteoporosis. Low bone density is a major cause of fractures. Data from the National Health and Nutrition Examination Survey, using a definition of osteoporosis developed by the World Health Organization, determined that up to 20% of white women over 50 have osteoporosis and up to 50% have low bone mass. Non-white women and men have lower rates of osteoporosis but contribute up to 25% of the fractures annually (Looker). Low trauma fractures at any site in the elderly are largely due to low bone mass. Hip fractures are the most devastating and costly osteoporotic fractures.” (NIH press release, 1998)
While osteopenia and osteoporosis are most often associated with aging, they can also be secondary to numerous diseases and/or therapies associated with these diseases. Aside from postmenopausal and age-related osteoporosis, osteoporosis can be heritable, endocrine-mediated, diet-related, drug-induced, disuse- or disease-related, or idiopathic (no identifiable cause). No class of drugs has been more often associated with osteoporosis than treatment with exogenous glucocorticoids, which are notorious for causing rapid onset of bone loss with ultimate osteopenia/osteoporosis, even at low doses.
Almost all currently available treatments for preventing progression of osteopenia/osteoporosis include drugs which are primarily antiresorptive including estrogens, bisphosphonates, and calcitonin (salmon or human). Additional therapies include calcium supplements, progesterone or progesterone analogs, and vitamin D and its analogs.
Calcitonin and calcitonin-gene related peptide have been of particular interest. Both are proteins secreted in abundance in the fetal circulation and are thought to be essential for bone growth in the fetus. Concentrations of both decline shortly after birth and remain low thereafter. While the physiologic role of each in adulthood is unclear, salmon and human calcitonin are known to inhibit resorption of bone and have found application as therapies for osteoporosis, Paget's disease of bone, hypercalcemia, and other diseases.
Although calcitonin has been available as a treatment for osteoporosis for a number of years, reports on its efficacy in prospective bone density studies have been variable, with many studies demonstrating either no or little improvement in bone density during chronic treatment with this drug. In an analysis of 16 studies, mean increase in spine bone mineral density (BMD) was reported to be 1.97% (Cardona).
Alendronate, a bisphosphonate, is perhaps the most commonly prescribed treatment for the treatment of bone loss diseases today. In the largest study conducted to date assessing efficacy of calcitonin vs. alendronate, only modest increases in BMD were observed in the total femur and lumbar spine during up to 1 year of therapy with calcitonin in postmenopausal women (Rosen). This study was designed to compare efficacy of alendronate to calcitonin when used for treatment of osteoporosis in postmenopausal women.
In the study, two-hundred and seventy-five postmenopausal women with low bone mass (low BMD), −2.0 standard deviations (SD) at lumbar spine (LS) or femoral neck (FN) and −1.0 SD at the other site) were randomized at 9 US sites to either blinded alendronate at 10 mg or matching placebo or open-label calcitonin at 200 IU daily. All patients received vitamin D at 400 IU daily and calcium at 1000 mg daily including diet and supplements. LS, FN and hip trochanter (HT) BMD were measured at baseline, 6 and 12 months.
The authors found calcitonin did not improve bone mineral density in long-term use and concluded as follows: “Treatment with alendronate produced significantly greater increases in BMD than did calcitonin at both LS and HT at 6 and 12 months (p<0.001) and at FN at 12 months (p=0.003). BMD changes with calcitonin were not statistically different from placebo at LS, HT or FN at either 6 or 12 months. Adverse experiences similar between alendronate and calcitonin were difficult to interpret for calcitonin due to open-label drug. In postmenopausal women with low bone mass, alendronate produced significantly greater increases in BMD than nasal calcitonin at one year at both lumbar spine and hip.”
In a second large multicenter study, it was observed that bone mass increases with calcitonin were short-lived (Downs). The Downs study compared the efficacy of alendronate and calcitonin at doses currently prescribed in the US. Postmenopausal women with osteoporosis (n=299) were randomized at 24 US sites to either blinded alendronate 10 mg or matching placebo or open-label calcitonin 200 IU daily. All patients received calcium at 1000 mg daily including diet and supplements and vitamin D at 400 IU daily. Lumbar spine (LS), femoral neck (FN) and hip trochanter (HT) BMD were measured at baseline, 6 and 12 months.
Treatment with alendronate produced significantly greater increases in BMD than did calcitonin at both LS and HT at 6 and 12 months (p<0.001) and at FN at 12 months (p=0.001). BMD changes with calcitonin were statistically different from placebo at FN at 6 (p=0.003) and 12 months (p=0.008) but were not significantly different at either LS or HT at 6 or 12 months. Again, it can be seen that the effects of calcitonin on bone density were only modest compared to placebo.
DHEA (dehydroepiandrosterone) is the principal steroid secreted by the fetal adrenal gland, with concentrations significantly higher than other circulating steroids. Its role in fetal physiology is poorly understood, but it is thought to serve as a precursor for other steroids, leading to androgen and estrogenic steroids. It has been reported that DHEA may be useful in the treatment of osteoporosis/osteopenia. U.S. Pat. No. 5,776,923 indicates that administration of DHEA to ovarectomized rats results in increased bone density. However, the administration of DHEA to humans to prevent bone loss or increase bone density is not a recognized treatment for osteoporosis/osteopenia by the medical community. Extensive clinical trial data from systemic lupus erythematous (SLE) patients being treated with DHEA, 200 mg administered daily, showed only slight improvement of BMD, both in patients receiving DHEA alone, or in combination with prednisone.
Thus, there continues to be a need for more effective treatments for subnormal BMD in diseases such as osteoporosis, steroid induced osteoporosis, immunosuppressant induced osteoporosis, osteopenia, Paget's disease, periodontal disease and hypercalcemia.